This invention relates to a multistage automatic planetary transmission gearing suitable for motor cars, particularly passenger cars, with the changing of gear stages being effected by centrifugal multiple plate disk clutches.
Known multistage automatic transmission gearings in which gear stages are changed by means of centrifugal clutches are simple, but their operating properties are not fully satisfactory, particularly at the beginning of gear stage changing at uniform speed of the vehicle without regard to load, and also the mutual dependence of the first phase of gear changing between the speed v.sub.1 to v.sub.2 (v.sub.1 being the speed at which a forceless contact of friction parts of the clutch occurs, and v.sub.2 being the speed at which the gear change clutch transmits a part of the torque) and in the second phase of gear stage changing within the range of speeds v.sub.2 to v.sub.3 (v.sub.3 being the speed at which a rigid coupling of the gear change coupling takes place) the second phase of changing taking place at a reduction of the revolutions of the engine from n.sub.2 to n.sub.3. The steepness of the function n.sub.2 -n.sub.3 in dependence on time must not jeopardize the continuity of changing; wherein the range of speeds v.sub.1 to v.sub.3 , where the efficiency of transmission of power is reduced due to slippage of the gear change clutch, inefficiency should not increase proportionally. These prior transmission gears are not suitable for more than two speed stages.
In automatic planetary transmission gearing in which the gear changing is accomplished by oil controlled clutches in the first and second phase of changing on the continuity of changing within a chosen narrow speed range v.sub.1 to v.sub.3 are eliminated by a hydrodynamic starting clutch, or by a hydrodynamic torque converter, at the price of a reduced efficiency of power transmission within the whole speed range of the vehicle except for the highest speed stage if the hydrodynamic element is at the highest speed stage, and at the price of higher costs and complexity of the transmission gear if the hydrodynamic element is connected to the highest speed stage. In the latter case fuel consumption is affected unfavorably and the operating properties are secured by rather hydraulic complicated and in recent times also electronic control means, the parts of which are costly and demanding as to technology and service.